Throughout the United States there is an increasing trend toward using value-added methods (VAMs) for high-stakes decisions. When policymakers use VAMs to identify, reward, and dismiss teachers, they may perpetuate the egg-crate model of schooling and undermine efforts to build instructional capacity schoolwide. At any time, in any school, some teachers are more knowledgeable, experienced, and skilled than others. Schools function best when they continuously leverage teachers' expertise so that all students in all classrooms are well served. Drawing from research about the incentives and norms that influence teachers' work within schools, this article illustrates what can happen when these methodologies are used to make job decisions and it identifies the hazards of using VAMs for this purpose. Contextualizing this within the larger discussion about performance evaluation systems, the article suggests how VAMs can be used productively as one source of information to promote improvement schoolwide.